I have 223k on my 2.5 and now it burns a little oil. Some of my friends suggested that I use heavier oil.
Right now I use 10w-40 for high mileage engine.
I was wondering if it would be ok to use 10w50 or anything else.

NO would be the answer

Thats not going to fix your problem and its going to be ultra thick going to the operating system for the valves- bad

Throw some smoke-b-gone or other stop leak- thickener

You can always fix the problem and keep on driving another 50-100k

Heavier oil isn't the answer. What's the definition of "now it burns a little oil"?

How many miles before it's a quart low? Is there visible smoke? When? Accelerating, decelerating or just killing mosquitoes while you drive?

Is it burning oil, or maybe leaking it?

There are a lot of variables, but using heavier oli isn't the right answer for any of them.

every 3k miles, i add a quart to keep it toped off all the time.
no heavy smoke or anything but spark plug # 3 and 4, i see oil. I already replaced spark plug seals twice recently.

If I need to fix this problem, what needs to be fixed?

May be the valve guide seals, a compression test will say where the oil is going
Have never heard of spark plug seals- what did you replace

It may be possible to add the spark plug extenders/covers to the 2 offended plugs, that protects the electrode from oil dripping down and when you start the engine- the oil blows onto the spark plug and fouls it. bummer.

if you remove the valve cover, there are five spark plug seals/gasket that you can replace to give the cover tight seal from oil to dip into the spark plug well.

Is the oil on the electrode end of the plug when you remove the plug, or are you talking about oil leaking onto the outside of the plug?

Inside could be rings or possibly valve seals. You mechanic can do a leak-down test to check the rings. Have someone follow you and observe your exhaust pipes. If you get a puff a blue smoke when you let up on the gas, that's usually a valve stem seal. When you take your foot off the gas the engine can suck some oil past a bad valve seal.

If the oil is on the outside of the plugs, you could just have some leaks. My wife's Honda was using a quart every 3 to 4,000 miles just from several small leaks.

thanks for your input. i usually see oil on the bottom part of the plug.
i have not seen any blue smoke.
i will do the leak test soon.